In this type of a conventional X-ray computed tomography, as shown in FIG. 1 by a solid line, a projectional distribution of X-ray is measured by X-ray detector c in such a way as X-ray beam is projected from X-ray source a toward a X-ray tested tissue b of body b. Then, as shown in FIG. 1 by a dotted line, X-ray source a and X-ray detector c are rotated by a desired angle of .alpha. (for example 1.degree.), and at this position X-ray beam is projected again toward X-ray tested tissue b of body, a projectional distribution of X-ray under the rotation of an angle of .alpha. is measured again, and several 60 to 360 times of similar operations are performed. Thereafter, data provided by these many projectional distributions of X-ray are calculated by Fourier transform or a convolution method, and a tomography of the X-ray tested tissue b of body is reproduced on the basis of a result of the processing.
However, in this type of a conventional X-ray computed tomography, it is necessary to have many projectional distributions of X-ray in order to reproduce a tomographic image of X-ray tested tissue b of body, resulting in providing such some problems as follows:
(1) Since a long period of time is needed (several seconds to several minutes) for sampling data, it is not possible to reproduce a tomographic image of a moving tested tissue b of a body.
(2) Exposure of X-ray shows a high value, resulting in that some bad effects might be applied to the tested tissue of body when the tested tissue b is a living thing such as a human body.
The present invention is provided to overcome these disadvantages and its object is to provide a reconstruction method of X-ray computed tomographic image in which a reconstruction image having a high accuracy or precision may be produced by using two projectional distributions of X-ray as data for reconstructing a tomographic image of the tested tissue.